In semiconductor manufacturing, Al circuits and Cu circuits are formed on silicon wafers by Al sputtering, Cu plating, and other means, but the higher integration levels and smaller sizes of semiconductor devices in recent years have been accompanied by a steady trend toward narrower wiring line widths and spaces between wiring lines (intervals).
The wiring patterns of Al circuits and Cu circuits are formed using photolithography techniques. For example, after uniformly coating a resin on an Al film, an exposure system called a stepper is used to print a pattern in the resin film, and by heat-hardening the resin film and removing needless portions, a removal-pattern resin film is formed on top of the Al film for wiring. Then an etching system is used to etch the Al film along the removal-pattern portion, and on removing the resin film, patterned Al wiring is obtained.
When wiring lines are in close proximity, signals in the lines interact each other; hence there is a need to eliminate interaction between wiring lines by filling areas between wiring lines and between stacked layers with low-dielectric constant insulating material. Conventionally, silicon oxide has been used as the insulating material for this purpose; but more recently materials known as low-k materials have been used as insulating films with still lower dielectric constants. Low-k insulating films are formed by dispersing the material in a dispersing medium in slurry form, which is used in spin-coating to form a uniform film; then photolithography techniques similar to those described above are employed in pattern formation, following by heat-calcining using a heater to harden the film.
Heat-hardening of resin film for photolithography and heat-calcining of low-dielectric constant insulating film such as low-k film is performed within a system called a coater-developer; as the heater, for example, a heater formed by enclosing SUS foil, which is a resistive heating element, between quartz glass plates is used. However, because there are problems, which are the thermal uniformity and durability, with such a heater, a heating device comprising a heater which affords excellent thermal uniformity and high durability has been sought.
On the other hand, CVD equipment used to form various thin films employ a ceramic heater, in which an Mo coil is embedded by hot-press sintering of AlN, Si3N4, or another ceramic material with high thermal conductivity and good corrosion resistance. The surface on the rear of the wafer-holding surface of this ceramic heater is bonded to one end of a cylindrical ceramic support member, the other end of which is supported by the chamber and sealed with an O-ring. Electrode terminals and lead wires to supply electrical power are poor corrosion resistant and housed within the cylindrical support member so as not to be exposed to the corrosive gas used within the chamber.
In recent years, Si wafer sizes have been increased in order to lower semiconductor manufacturing costs, and wafer diameters are moving from 8 inches to 12 inches. Consequently in coater-developers used for heat-hardening of resin films for photolithography and heat-calcining of low-k and other low-dielectric constant insulating films, there are intensified demands for thermal uniformity of the heater. Specifically, it is required that the thermal uniformity of the wafer-holding surface of the heater be within ±1.0%, and preferably within ±0.5%.
In general, by using ceramic material with high thermal conductivity embedded a resistive heating element as a heater, the heat generated by the resistive heating element is diffused within the ceramic material, and thermal uniformity can be maintained at the wafer-holding surface. Further, by using ceramic material with high heat resistance, a heater with excellent durability is obtained.
For example, when a configuration similar to that of an AlN ceramic heater used in CVD equipment is employed, one end of a cylindrical AlN support member is bonded to the center of the rear surface opposite the wafer-holding surface, and the other end is supported by bonding to the chamber. In addition, the electrode terminals and lead wires for the supply of power are housed within the cylindrical support member.
However, both ends of the cylindrical support member supporting the ceramic heater are hermetically sealed, and the interior is isolated from the interior of the chamber, so that the outer periphery is exposed to the reduced-pressure atmosphere within the chamber, while the inner periphery is exposed to an air atmosphere at atmospheric pressure. In this case, thermal transmission through air at atmospheric pressure is greater, so that the temperature is lower on the inner periphery of the support member than on the outer periphery, and this effect also appears at the wafer-holding surface; as a result, it is not able to achieve the required thermal uniformity of within ±1.0%.
When the interior of the cylindrical support member is bonded and hermetically sealed so as to be completely isolated from the chamber, if the thermal expansion coefficients of the ceramic heater and that of a support member are different, then the difference in thermal shrinkage during cooling processes causes thermal stresses, and cracks tend to appear in the brittle ceramic material. In order to prevent this, the support member must be fabricated from the same material with high thermal conductivity as the ceramic heater. However, in this case, heat generated by the ceramic heater easily escapes via the support member, and the temperature of the ceramic heater is greatly reduced at the joined portion, so that it cannot maintain thermal uniformity.